I don't have the game so I can't tell you what the eye represents. I found this mention of it in a player review:
What is the purpose of the eye icon? I noticed that clicking it causes some of the tiles to fade out and become unmovable. So what advantage/disadvantage does that have for the player?
So apparently you are not alone in not understanding it.
I found this forum thread discussing level 5 of Legendary Slide:
Legendary Slide Level 5 See if that helps you.